 (function(window, document) {
     //定义画布宽高和生成点的个数
     var WIDTH = window.innerWidth,
         HEIGHT = window.innerHeight,
         POINT = 75;

     var canvas = document.getElementById('canvas');
     canvas.width = WIDTH,
         canvas.height = HEIGHT;
     var context = canvas.getContext('2d');
     context.strokeStyle = 'rgba(0,0,0,0.02)',
         context.strokeWidth = 1,
         context.fillStyle = 'rgba(0,0,0,0.05)';
     var circleArr = [];

     //线条：开始xy坐标，结束xy坐标，线条透明度
     function Line(x, y, _x, _y, o) {
         this.beginX = x,
             this.beginY = y,
             this.closeX = _x,
             this.closeY = _y,
             this.o = o;
     }
     //点：圆心xy坐标，半径，每帧移动xy的距离
     function Circle(x, y, r, moveX, moveY) {
         this.x = x,
             this.y = y,
             this.r = r,
             this.moveX = moveX,
             this.moveY = moveY;
     }
     //生成max和min之间的随机数
     function num(max, _min) {
         var min = arguments[1] || 0;
         return Math.floor(Math.random() * (max - min + 1) + min);
     }
     // 绘制原点
     function drawCricle(cxt, x, y, r, moveX, moveY) {
         var circle = new Circle(x, y, r, moveX, moveY)
         cxt.beginPath()
         cxt.arc(circle.x, circle.y, circle.r, 0, 2 * Math.PI)
         cxt.closePath()
         cxt.fill();
         return circle;
     }
     //绘制线条
     function drawLine(cxt, x, y, _x, _y, o) {
         var line = new Line(x, y, _x, _y, o)
         cxt.beginPath()
         cxt.strokeStyle = 'rgba(0,0,0,' + o + ')'
         cxt.moveTo(line.beginX, line.beginY)
         cxt.lineTo(line.closeX, line.closeY)
         cxt.closePath()
         cxt.stroke();

     }
     //初始化生成原点
     function init() {
         circleArr = [];
         for (var i = 0; i < POINT; i++) {
             circleArr.push(drawCricle(context, num(WIDTH), num(HEIGHT), num(15, 2), num(10, -10) / 16, num(10, -10) / 16));
         }
         draw();
     }

     //每帧绘制
     function draw() {
         context.clearRect(0, 0, canvas.width, canvas.height);
         for (var i = 0; i < POINT; i++) {
             drawCricle(context, circleArr[i].x, circleArr[i].y, circleArr[i].r);
         }
         for (var i = 0; i < POINT; i++) {
             for (var j = 0; j < POINT; j++) {
                 if (i + j < POINT) {
                     var A = Math.abs(circleArr[i + j].x - circleArr[i].x),
                         B = Math.abs(circleArr[i + j].y - circleArr[i].y);
                     var lineLength = Math.sqrt(A * A + B * B);
                     var C = 1 / lineLength * 7 - 0.009;
                     var lineOpacity = C > 0.03 ? 0.03 : C;
                     if (lineOpacity > 0) {
                         drawLine(context, circleArr[i].x, circleArr[i].y, circleArr[i + j].x, circleArr[i + j].y, lineOpacity);
                     }
                 }
             }
         }
     }

     //调用执行
     init();
     setInterval(function() {
         for (var i = 0; i < POINT; i++) {
             var cir = circleArr[i];
             cir.x += cir.moveX;
             cir.y += cir.moveY;
             if (cir.x > WIDTH) cir.x = 0;
             else if (cir.x < 0) cir.x = WIDTH;
             if (cir.y > HEIGHT) cir.y = 0;
             else if (cir.y < 0) cir.y = HEIGHT;

         }
         draw();
     }, 16);
 })(window, document);